Show toolbar for docker's internal IP address

Fixes #1854

debug_toolbar/middleware.py

@@ -3,6 +3,7 @@
 """
 
 import re
+import socket
 from functools import lru_cache
 
 from django.conf import settings
@@ -12,14 +13,32 @@
 from debug_toolbar.toolbar import DebugToolbar
 from debug_toolbar.utils import clear_stack_trace_caches
 
+# See https://docs.python.org/3/library/socket.html#socket.gaierror
+SOCKET_SERV_NAME_NOT_KNOWN = 8
 _HTML_TYPES = ("text/html", "application/xhtml+xml")
 
 
 def show_toolbar(request):
     """
     Default function to determine whether to show the toolbar on a given page.
     """
-    return settings.DEBUG and request.META.get("REMOTE_ADDR") in settings.INTERNAL_IPS
+    internal_ips = settings.INTERNAL_IPS.copy()
+
+    try:
+        # This is a hack for docker installations. It attempts to look
+        # up the IP address of the docker host.
+        # This is not guaranteed to work.
+        docker_ip = (
+            # Convert the last segment of the IP address to be .1
+            ".".join(socket.gethostbyname("host.docker.internal").rsplit(".")[:-1])
+            + ".1"
+        )
+        internal_ips.append(docker_ip)
+    except socket.gaierror as err:
+        # It's fine if the lookup errored since they may not be using docker
+        if err.errno != SOCKET_SERV_NAME_NOT_KNOWN:
+            raise
+    return settings.DEBUG and request.META.get("REMOTE_ADDR") in internal_ips
 
 
 @lru_cache(maxsize=None)

docs/changes.rst

@@ -4,6 +4,9 @@ Change log
 Pending
 -------
 
+* Automatically support Docker rather than having the developer write a
+  workaround for ``INTERNAL_IPS``.
+
 4.3.0 (2024-02-01)
 ------------------
 

docs/installation.rst

@@ -145,12 +145,10 @@ option.
 
 .. warning::
 
-    If using Docker the following will set your ``INTERNAL_IPS`` correctly in Debug mode::
-
-        if DEBUG:
-            import socket  # only if you haven't already imported this
-            hostname, _, ips = socket.gethostbyname_ex(socket.gethostname())
-            INTERNAL_IPS = [ip[: ip.rfind(".")] + ".1" for ip in ips] + ["127.0.0.1", "10.0.2.2"]
+    If using Docker, the toolbar will attempt to look up your host name
+    automatically and treat it as an allowable internal IP. If you're not
+    able to get the toolbar to work with your docker installation, review
+    the code in ``debug_toolbar.middleware.show_toolbar``.
 
 Troubleshooting
 ---------------

tests/test_integration.py

@@ -2,6 +2,7 @@
 import re
 import time
 import unittest
+from unittest.mock import patch
 
 import html5lib
 from django.contrib.staticfiles.testing import StaticLiveServerTestCase
@@ -66,6 +67,14 @@ def test_show_toolbar_INTERNAL_IPS(self):
         with self.settings(INTERNAL_IPS=[]):
             self.assertFalse(show_toolbar(self.request))
 
+    @patch("socket.gethostbyname", return_value="127.0.0.255")
+    def test_show_toolbar_docker(self, mocked_gethostbyname):
+        with self.settings(INTERNAL_IPS=[]):
+            # Is true because REMOTE_ADDR is 127.0.0.1 and the 255
+            # is shifted to be 1.
+            self.assertTrue(show_toolbar(self.request))
+        mocked_gethostbyname.assert_called_once_with("host.docker.internal")
+
     def test_should_render_panels_RENDER_PANELS(self):
         """
         The toolbar should force rendering panels on each request